1. Field of the Invention
The invention is directed to a method and apparatus for first treating a well production zone, such as, for example, removing lost circulation material temporarily plugging perforations in the well and, thereafter, selectively gravel packing said well.
2. Description of the Prior Art
After a well has been drilled, it is completed by typically running into the well a string of casing which is cemented in place in the well. Thereafter, when the well is cased, perforations are shot through the casing adjacent the selected production zone to permit fluid flow to the top of the well. However, in order to prevent contaminants and to assist in controlling the well to abate a blowout, prior to removal of the equipment which is utilized to perforate the casing, a lost circulation material, which typically may be a solution of carboxymethylcellulose, guar gum, or other lost circulation material which is well known to those skilled in the art, is circulated into the well and spotted across the perforations for temporarily sealing them or, in the case of uncased wells, is spotted across the open production zone. Such lost circulation material is also required to protect the perforations and the porous production zone from the adverse effects of fluids which are required to be injected into the well during and after removal of the perforating equipment to maintain the well in an overbalanced condition for control thereof prior to effective setting of other completion equipment.
Other treatment of wells includes fracturing, acidizing and similar stimulation techniques.
In wells in which gravel packing is required as part of the completion operation to prevent particulate matter contained within the production flow from entering the completion equipment to the top of the well, it is necessary to gravel pack said wells by placing gravel exteriorly of the completion equipment and adjacent the perforations. Such gravel will be sized to prevent particulate matter within the production fluids from passing interiorly through a ported, slotted or screen member of the completion equipment which, itself, is sized to prevent the gravel from passing interiorly into the completion equipment, yet permitting the production fluid to freely pass therethrough into the completion equipment for production to the top of the well.
Prior to such gravel packing operation, the lost circulation material must be removed from the perforations or the open hole production zone. It has been found that prior apparatuses and methods for removal of the lost circulation material have not been entirely satisfactory because they inject the lost circulation material removal fluid in such a manner that it contacts the perforations at their uppermost portion and fluid is induced through such uppermost perforations, thence through the production zone, resulting in lost circulation. Once circulation is lost in such a manner, it is impossible, or extremely difficult, to remove the remaining lost circulation material in the other or lowermost perforations.
The present invention is directed to abating this problem by providing a method and means for removal of the lost circulation material or other treatment material and treatment fluid in a manner that the lost circulation material removal fluid first contacts the lowermost of the perforations before contact with the uppermost perforations. In this manner, the lowermost perforations are cleared and, thereafter, the lost circulation material removal fluid is thereafter permitted to treat the uppermost perforations, from top to bottom. Lost circulation will not occur in such a procedure because any lost circulation material within and behind the perforations which is being removed during the first step, i.e. bottom to top of the lowermost perforations, will fall down into the treated void. Such shifting of the lost circulation material can also be expected to occur when the lost circulation material is treated from top to bottom by contact of the lost circulation treating fluid with the uppermost perforations thereby eliminating, or greatly reducing, the hazards of lost circulation.
The present invention, in essence, provides apparatus and method for removal of a treatment fluid from a production zone by first directing a removal fluid in one direction to contact one end of the production zone and, thereafter by directing the removal fluid in another direction to contact the other end and remainder of the production zone to remove the balance of the treatment fluid or treatment material, i.e., lost circulation material.
The present method and apparatus also has the desired feature of thereafter permitting gravel packing of the production zone without retrieval of the equipment to the top of the well and subsequent tripping into the well with the gravel packing equipment.